Transfer switch for tap changers for regulating transformers



March 16, 1965 A. BLEIBTREU 3, 7 97 TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS Filed Jan. 31, 1963 5 Sheets-Sheet l March 1965 A. BLEIBTREU 3,174,097

TRANSFER SWITCH FOR TAP CHANGER-S FOR REGULATING TRANSFORMERS Filed Jan. 31, 1963 5 Sheets-Sheet 2 March 16, 1965 A. BLEIBTREU TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS Filed Jan. 31, 1963 5 Sheets-Sheet 3 INVENTOP March 16, 1965 A. BLEIBTREU TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS 5 Sheets-Sheet 4 Filed Jan. 31, 1965 INVEAUOR.

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March 16, 1965 A. BLEIBTREU TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS 5 Sheets-Sheet 5 Filed Jan. 31, 1963 FIG IE INVENTOI? I United States Patent TRANSFER SWITCH FOR TAP CHANGERS FOR REGULATING TRANSFORMERS Alexander Bleihtreu, Regensburg, Germany, assignor to Mascliinenfabrik Reinhausen Gebriider Scheubeck K.G., Regensburg, Germany Filed Jan. 31, 1963, 801'. No. 255,291

Claims priority, application Germany, Feb. 8, 1962, M 51,739; May 17, 1962, M 52,886

Claims. (Cl. 32343.5)

This invention is concerned with transfer switches for tap-changing regulating transformers.

It is a general object of this invention to provide improved transfer switches for tap-changing regulating transformers capable of effectively handling relatively high load currents and also overload currents.

It is another object of this invention to provide improved transfer switches of the type wherein each switching operation comprises the formation of two serially related points of break, which points of break have a significant spatial separation, thus resulting in a reduction of the recovery voltage per break, and minimizing the danger of contamination of some points of break by products of, arcing formed at other points of break.

It is another object of this invention to provide an improved circuitry for transfer switches for tap-changing regulating transformers which circuitry makes it possible to substantially increase the switching rating of such transfer switches to the order of say 200% to 300% of the rated current carrying capacity thereof.

Another object of this invention is to provide improved transfer switches for tap-changing transformers wherein pitting of the contacts and erosion of the contacts is precluded even in case of onerous duty cycles involving frequent switching operations and large overload currents.

Another object of this invention is to provide improved transfer switches for so-called Jansen type tap-changing regulating transformers.

Transfer switches according to the present invention may be constructed either for single phase service or for polyphase service.

Tap-changing regulating transformers include selector switches and transfer switches. The selector switches serve the purpose of selecting a particular tap on a tapped transformer winding intended to be connected into an electric circuit. Selector switches are not required to interrupt, or close, on current carrying circuits. This task is performed by the transfer switches. The latter perform all switching operations under load. Therefore all arcing is kept away from the selector switches and occurs only at the transfer switches. It is, therefore, of considerable importance that the transfer switches be designed to effectively cope with power arcs resulting from load switching operations and overload switching operations.

The above and additional objects and advantages of the invention will become more apparent from the ensuing description thereof when read in connection with the ac companying drawings wherein:

FIG. 1 shows a prior art transfer switch known as the Pennant transfer switch and the voltage vector diagram pertaining to that kind of transfer switch;

FIG. 2 shows the prior art transfer switch known as the Flag transfer switch and the voltage vector diagram pertaining to that kind of transfer switch;

FIG. 3 shows the prior art transfer switch known as Flag-Pennant transfer switch and the voltage vector diagram pertaining to that kind of transfer switch;

FIGS. 4-7, inclusive, show diagrammatically a transfer switch embodying the present invention in various successive operating positions thereof;

FIG. 8 is mainly a vertical section through a transfer switch embodying the present invention, some parts thereof being shown in front elevation rather than in vertical section;

FIG. 9 is a horizontal section through the structure of FIG. 8 showing the main contacts and the auxiliary contacts thereof in top-plan view;

FIG. 10 shows a detail of FIG. 8 on a substantially larger scale;

FIG. 11 is a section along 11-1l of FIG. 10; and

FIG. 12. is a horizontal section through the structure of FIG. 8 taken at a lower level than the section shown in FIG. 9.

The aforementioned terms Pennant transfer switch, Flag transfer switch and Flag-Pennant transfer switch have been coined by Bernhard Jansen to whom the development of these three types of transfer switches is due. The reasons why Bernhard Jansen coined these terms will be readily apparent from the ensuing consideration of FIGS. 13. For reasons of brevity the term P-transferswitch will be used hereinafter as an abbreviation of the term Pennant transfer switch, the term F-transfer-switch will be used as an abbreviation of the term Flag transfer switch and the term FP-transfer-switch will be used as an abbreviation of the term Flag-Pennant transfer switch.

FIGS. 1-3 show a portion T of a tapped transformer winding. The P-transfer-switch comprises four movable contacts 1, 2, 3, 4. A cylindrical contact support 6a of insulating material supports four fixed contacts adapted to be cooperatively engaged by the aforementioned movable contacts 1, 2, 3, 4. The taps U U of the tapped portion of winding T, are directly connected by appropriate leads to the outer or fixed main contacts of the P- ransfer-switch. The taps U U are further connected by the intermediary of ohmic resistors R to the inner or fixed auxiliary contacts of the P-transfer-switch. The movable contacts land 3, on the one hand, and the movable contacts 2 and 4, on the other hand, form part of separate or different contact operating systems. This makes it possible to adjust the operating times of movable contacts 1 and 3 relative to the operating times of movable contacts 2 and 4. In the position of the contacts shown in FIG. 1 tap U is directly connected to the load, the flow of the load current being indicated by a small arrow. Changing the connection of the load from tap U, to tap U involves a closing operation of movable auxiliary contact 3 preceding the separation of the left movable main contact 1 from its cooperating fixed main contact. Since the fixed auxiliary contact cooperating with the movable auxiliary contact 3 is connected to tap U by the intermediary of right resistor R, the closing operation of contact 3 gives rise to a circulating current. This circulating current is superimposed upon the load current. As mentioned above, contact 1 parts subsequent to engagement by movable contact 3 of its cooperating fixed contact. Parting of contact 1 from its cooperating fixed contact is followed by engagement by contact 4 of its fixed cooperating contact and by separation of contact 2 from its fixed cooperating contact. The gist of P-transfer-switches of which FIG. 1 shows but one of many possible embodiments resides in the fact that prior to interrupting a load circuit including a given tap, another pre-selected tap is being connected into the load circuit by the intermediary of an ohmic resistor. As a result, the difference in potential between taps U and U gives rise to a circulating current and it is the algebraic sum of this circulating current and of the load current which must be interrupted by the P-transfer-switch. This is a relatively onerous interrupting duty. On the other hand, operation of a P-transfer-switch has little efiect upon the system voltage.

Referring now to FIG. 2, the same reference characters have been applied in FIG. 2 as in PEG. 1 to indicate like parts. The F-transfer-switch shown in FIG. 2 differs from the P-transfer-switch shown in FIG. 1 in regard to the se quence of switching operations. In the F-transfer-switch the movable contact 1 parts from its cooperating fixed contact subsequent to engagement by movable contact 2 of its cooperating fixed contact which is connected by the intermediary of left ohmic resistor R with tap U of transformer winding T Hence no circulating current is established incident to engagement between the movable contact 2 and its cooperating fixed contact. The gist of an F-transfer-switch is seen in that in such a transfer switch a contact is closed to connect a resistance into the circuit extending from the active tap to the load before another contact is closed establishing a current path from a preselected tap (the one to which a direct connection is to be made) to the load. Since an F-transfer-switch does not give rise to the flow of circulating currents, only the load current is interrupted when movable contact 1 parts from its cooperating fixed contact. While the interrupting duty or switching duty of an F-transfer-switch is relatively easy, its reaction on the system voltage is relatively significant.

Referring now to FIG. 3 illustrating a FP-transferswitch, the fixed contacts thereof are arranged on a cylindrical contact support 6a and the movable contacts 1, 2 5, 6 are operated by two separate lever systems. One of these lever systems includes contacts 1, 3 and 5 and the other of these lever systems includes contacts 2, 4 and 6. The tap U is directly connected to the fixed contact cooperating with movable contact 1. Tap U is further connected to the fixed contact cooperating with movable contact 2 by the intermediary of an ohmic resistor R and to the fixed contact cooperating with movable contact 3 by the intermediary of ohmic resistor R In a similar fashion tap U is directly connected to the fixed contact cooperating with movable contact 6 and tap U is connected by the intermediary of ohmic resistors R R with the fixed contacts cooperating, respectively, with movable contacts 4 and 5. Movable contact 1 parts from its cooperating fixed contact after movable contact 3 has engaged its cooperating fixed contact. Upon completion of the aforementioned sequential operations of movable contacts I and 3 tap U i.e. the tap to be disconnected and resistors R and R are connected into the load circuit, resistors R and R being connected in parallel. Thereupon movable contact l engages its cooperating fixed contact and movable contact 2 parts from its cooperating fixed contact. Finally fixed contact 6 engages its cooperating fixed contact and movable contact 4- parts from its cooperating fixed contact. In this position of the FP- transfer-switch tap U is entirely disconnected, and tap U is connected into the load circuit of the transformer. Referring now to the vector diagram at the right of FIG. 1, reference letter U has been applied to indicate the transformer voltage, i.e. the voltage of the windings of the transformer which are not involved in the tap-changing operation, reference characters Uw and UWg have been applied to indicate the vectors of the voltages across the resistors which are inserted into the circuit during a tap changing operation and the reference character U has been applied to indicate the vector of the voltage between the two taps U and U The angular relation of the above vectors depends upon the phase angle prevailing in the particular circuit under consideration. However this phase angle may be, the vector diagram of the voltages involved is generally in the shape of a pennant, the vector U forming the pole thereof. Hence the term Pennant transfer switch or P-transfer-switch which was coined for the transfer switch structure shown in FIG. 1 and described in connection with that figure.

In the vector diagram to the right of FIG. 2 reference letter U has been applied to indicate the vector of the Voltage across the windings of the transformer not involved in the tap changing operation, reference character U has been applied to indicate the vector of the voltage across taps U and U and reference characters Uw and Uw have been applied to indicate the vectors of the recovery voltages across the resistors which are inserted into the circuit during the tap-changing operation. The angular relation of the above vectors depends again upon the phase angle b prevailing in the particular circuit under consid eration, and the vector diagrams of FIGS. 1-3 have been drawn assuming that cos =.8. Interconnecting the ends of the voltage vectors shown in FIG. 2 by appropriate lines results in an outline which is generally in the shape of a flag. Hence the term Flag transfer switch or F- transfer-switch which Was coined for the transfer switch structure shown in FIG. 2 and described in connection therewith.

In the vector diagram to the right of FIG. 3 showing the voltage vectors of the transfer switch shown in FIG. 3 reference characters Uw Uw and Uw have been applied to indicate the vectors of the recovery voltages across the various resistor combinations which are inserted into the load circuit during a tap-changing operation. Interconnecting the ends of the voltage vectors by appropriate lines results in an outline which is generally in the shape of a combination of a flag and a pennant. Hence the term Flag-Pennant transfer switch or FP-transfer-switch which was coined for the kind of transfer switches shown to the left of FIG. 3 and described in connection therewith.

Prior art P-transfer-switches as well as prior art F-transfer-switches and prior art FP-transfer-switches are capable of safely switching currents in the order of the rated current carrying capacity, and have a life commensurate to that of the regulating transformer with which they are associated. However, such transformer switches are not capable of switching effectively overload currents of, say 2 to 3 times the rated current. Switching of currents of such magnitude is conducive to excessive arcing tending to cause short-circuits between immediately adjacent transformer taps with resulting danger to the transfer switch as well as to the regulating transformer itself. The novel transfer switch diagrammatically shown in FIGS. 4-7 removes the aforementioned limitations of prior art transfer switches.

The transfer switch shown in FIGS. 4-7 comprises six movable contact bridges 1', 2, 3, 4', 5, 6'. These contact bridges may be arranged on cylindrical segments. Contact bridges 1', Z 5', d are adapted to cooperate with a system of upper fixed contacts 31 and with a system of lower fixed contacts 30. The transfer switch is associated with a tapped transformer winding of which but one section situated between two taps U and U has been shown. Tap U is directly connnected by a lead to fixed contact 3t? cooperating with contact bridge 1'. Tap U is further connected by the intermediary ohmic resistors R and R to the fixed contacts 36 cooperating with contact bridge 2' and 3', respectively. Tap U is directly connected by a lead to fixed contact 3t! cooperating with contact bridge 6'. Tap U is further connected by the intermediary of ohmic resistors R and R to the fixed contacts 30 cooperating with contact bridge 4' and 5, respectively. The fixed contacts 31 cooperating with contact bridges 2', 3', 4 and 5 are conductively interconnected by lead 2100.

Assuming that the transformer winding of which the section between taps U and U forms a part is a phase winding of a three phase Y-connected transformer, then lead tilt? is conductively connected to the neutral point of the Y-connected transformer. This has been indicated by placing an inverted Y adjacent to lead 100.

The fixed contact 31 cooperating with contact bridge 1 is conductively connected to the fixed contact 30 cooperating with contact bridge 2' by lead 101. In a like fashion the fixed contact 31 cooperating with contact bridge 6' is conductively connected to the fixed contact 3% cooperating with contact bridge 5' by a lead 101.

In the position of the parts shown in FIG. 4 tap U is active and tap U is inactive. An electric circuit is established which includes tap U fixed contact 30 cooperating with contact bridge 1, contact bridge 1, fixed contact 31 cooperating with contact bridge 1', lead 101, fixed contact cooperating with contact bridge 2', contact bridge 2, fixed contact 31 cooperating with contact bridge 2', lead 100, neutral point.

The first tap-changing step which is shown in FIG. 5 consists in engagement of fixed contacts 31, 30 by their cooperating contact bridge 3' and in separation of contact bridge 1' from its fixed cooperating contacts 31, 3%. Separation of contact bridge 1 from its fixed cooperating contacts 31, 3% results in the formation of two series breaks in the circuit. These series breaks are shunted by ohmic resistor R resulting in instability of the two arcs formed at the two points of break.

The second tap-changing step which is shown in FIG. 6 consists in engagement .of the fixed contacts 31, 3d cooperating with contact bridge 4' by the latter. The contact operating mechanism may be designed in such a way that sufficient time elapses to allow extinction of the arcs formed at the two aforementioned breaks at contact bridge ll before contact bridge 4' engages its cooperating fixed contacts 31, 39. This calls for are extinction at the first natural current zero and can readily be achieved if the current is not in excess of the rated load current of the transfer switch. Upon engagement of the fixed contacts 31, 30 cooperating with the contact bridge 4 by the latter a current path for a circulating current is established which current path comprises tap U serially connected resistors R and tap U Another current path which exists at this point of time extends from tap U through left resistor R contact bridge 2, and lead lift) to the neutral point of the Y-connected system.

The third tap-changing step which is shown in FIG. 7 consists in engagement of the fixed contacts 31, 30 cooperating with the movable contact bridge 5 by the latter and in separation of the movable contact bridge 3' from its fixed cooperating contacts 31, 30. Separation of contact bridge 3 from its fixed cooperating contacts 31, 36 results in interruption of the current path of the circulating current. The main current path established by the third tap-changing step includes tap U resistors R and R in parallel, contact bridges 5 and 4' in parallel, lead lift), and the neutral point of the Y-connected system.

The fourth and final tap-changing step consists in parting of contact bridge 4 from its cooperating fixed contacts 31, 3t and engagement by contact bridge 6 of its cooperating fixed contacts 31, 39. This establishes a direct current path including tap U contact bridge 6', lead 1% and the neutral point of the Y-connected system.

Some of the tap-changing steps referred-to above include two switching operations. There is a total of six switching operations as follows: contact bridge 3 closes; contact bridge 1' opens; contact bridge 4 closes; contact bridge 2 opens; contact bridge 6 closes; contact bridge 4- opens.

As mentioned above, are extinction can readily be achieved at the first natural current zero at the points of break formed by cont-act bridge 1' if the. current flowing through contact bridge 1' is equal to, or not substantially in excess of, the rated load current of the transfer switch. If the current carried by contact bridge l is significantly larger, the arcing time is longer and arcing continues at the two breaks formed between contact bridge 1 and its fixed cooperating contacts 31, 30 while contact bridge 4 performs its closing operation. Under extremely severe switching conditions the arcing time at the two breaks formed contact bridge 1 and its two cooperating fixed contacts 31, 30 may extend up to the points of time at which contact bridges 5' and ti perform their respective closing operation.

Normally excessive arc duration at one of the points of break of a transfer switch is a danger condition likely to result in a short-circuit between two immediately adjacent taps. This danger is, however, avoided in the transfer switch of FIGS. 4-7. Assuming that the arcs formed at the two points of break of contact bridge 1' are not extinguished at the times contact bridge 4 engages its cooperating fixed contacts 31, 30 and contact bridge 2 parts from its cooperating fixed contacts 31, 3d. Parting of contact bridge 2 from its cooperating fixed contacts 31, 30 results in the formation of two breaks which are serially related to the two breaks formed by contact bridge 1'. Formation of these two additional breaks greatly increases the total or aggregate arc voltage and is thus conducive to more rapid arc extinction. The left resistor R shunts the two breaks formed between con tact bridge 1 and its cooperating fixed contacts 31, 30.

The design of the transfer switch of FIGS. 4-7 may be carried out in such a way that the length of the two breaks formed between contact bridge 1 and its cooperating fixed contacts 31, 3 exceeds the length of the two breaks formed by contact bridge 2' and its cooperating contacts 31, 30. Under such circumstances, in case of a restrike, or re-ignition, the dielectric breakdown of the two breaks formed by contact bridge 2' will precede the dielectric breakdown of the two breaks formed by contact bridge 1'. In case of a dielectric breakdown of the two breaks formed by contact bridge 2, two parallel current paths are established of which one comprises resistor R and contact bridge 2, and the other comprises resistor R and contact bridge 3. The voltage drop across resistor R and contact bridge 3' limits the flow of current through resistor R and contact bridge 2', and the voltage drop across resistor R and contact bridge 2'-which is small on account of the limitation of the flow of current through resistor R -liinits the recovery voltage across the two series breaks formed by contact bridge 1'. This, in turn, minimizes the danger of a dielectric breakdown of the two series breaks formed by contact bridge 1.

It will be apparent from the foregoing that transfer switches of the kind illustrated in FIGS. 4-7 increase their interrupting or switching capacity automatically if arcing persists on the two first-formed breaks on account of the presence of a current in excess of the med load current of the transfer switch.

it will be further apparent from the foregoing that transfer switches embodying the present invention operate as FP-transfer-switches as long as the current to be switched is in the order of the rated load current, and that they operate as P-transfer-switches having four serially related breaks if the current to be switched substantially exceeds the rated load current.

FIGS. 8-12, inclusive, refer to a preferred structural embodiment of the transfer switch diagrammatically illustrated in FiGS. 4-7.

The transfer switch shown in FIGS. 8-12 comprises a cylindrical tank 1 accommodating in the upper portion thereof the coaxial cylindrical transfer switch housing 2", while the lower portion of tank 1 houses the switching resistors R R R R Tank 1 contains a body of oil (not shown) and is preferably made of an appropriate casting resin. Terminals 4 and 5" are integral with tank 1'. Terminals 5 are intended to connect the transfer switch to the selector switch of the regulating transformer, and terminals 4 are intended to connect the transfer switch to the neutral point of the transformer. The aforementioned terminals are arranged in pairs in view of the high current carrying duty imposed upon these parts. If tank It is made of a casting resin terminals 4 and 5 are formed by inserts in the casting.

Flange element 6 is arranged in the upper portion of transfer switch housing 2. Element 6" is provided with contacts 6a cooperatively engaging with terminals t". A structure substantially in the shape of a squirrel-cage is suspended on flange element 6" by means of screws 10''. The above mentioned structure substantially in the shape of a squirrel-cage comprises the upper guide plate '7", the lower guide plate 8" and the conductive vertical bars 9" extending parallel to the common axis of tank 1" and housing 2". The upper end plate 12 and the lower end plate 13 are fixedly mounted upon operating shaft ll which is arranged in coaxial relation to tank 1 and housing 2". Rod 16 is spaced from shaft ll and extends parallel to shaft 11". The upper end and the lower end of rod 16 is loosely guided by the upper end plate 12" and the lower end plate 13'', respectively. The upper end of rod 16 is mechanically connected to the upper end plate 12" by means of a helical tension spring 14". In like fashion the lower end of rod 16" is mechanically connected to the lower end plate 13 by means of a helical tension spring Reference numeral 17" has been applied to indicate a plurality of upper contact operating arms and reference numeral 13 has been applied to indicate a plurality of lower contact operating arms. Each contact operating arm 17', 18 has a radially inner bearing and a radially outer bearing. Rod 16" extends through the radially inner bearings of contact operating arms l7", 18'. The radially outer ends of each pair of contact operating arms l7", 18 support a vertical shaft Zll which, in turn, supports pivotally a contact carrier 19'". Each contact carrier 19 is provided with axially outer bearings 1% and a central bearing 1% for receiving one of a plurality of vertical shafts 21" (see FIG. 10). Contact carriers 19 support contact bridges 2h" which-since supported by contact carriers 19"are adapted to be pivoted about vertical shafts 2E". The aforementioned upper and lower guide plates '7", 3 are provided with radially extending slots or grooves 22" and 23", respectively, engaged by and guiding the upper and the lower ends of contact carriers 19''. Because of this function of plates 7" and 8 the same have been referred to as guide plates. The contact carriers 19 are provided with upper grooves 24" and with lower grooves 25 intended for insertion of contact bridges 2t)" into the same. The contact bridges 2d of FIGS. 8-12 are the same parts to which reference characters 1', 2 5, 6 have been applied in FIGS. 4-7. Grooves 24 and 25 are sufiiciently large to provide a predetermined amount of clearance between contact carriers 19 and contact bridges Each contact bridge is provided with a pair of horizontal dead-end passageways each receiving a helical spring for biasing a steel ball 26". An insulating plate 28 arranged at the radially outer surface of each contact carrier 19" is provided with a pair of concave recesses 27" adapted to be engaged by steel balls 26'. Thus each of the contact bridges 20" is firmly yet resiliently held in position in its respective contact carrier 19". Each of the aforementioned insulating plates 23 engages a concave recess 29" in one of the contact carriers l9 and each of the contact bridges 29" has a convex projection on its back engaging recess 29 in one of the contact carriers 19 and one of the insulating plates 28, respectively. Grooves 24" and are provided with insulating inserts 24a and 25a for insulating contact bridges 20" from the contact carriers 19" at the upper and lower points where the former are inserted into the latter. The upper end of each contact bridge Ed and the lower end of each contact bridge 20" is adapted to cooperate with a pair of fixed contacts 31 and 30. Contacts 30 and 31 are supported by the wall of the switch housing 2 and include terminal elements which are arranged on the radially outer surface of the switch housing 2". Pairs of fixed contacts 31, 38 are arranged in vertically extending channel members 32 insulating contiguous pairs of contacts 31, 3t) from each other. Because of the provision of channel-shaped insulating barriers 32 the angular spacing of pairs of contacts 31, 3th may be small, and yet fiashovers between pairs of contacts 31, 3.0 which are at different potentials are effectively precluded by the presence of channel-shaped barriers 32".

The circuitry of FIGS. 4-7 calls for the provision of six contact carriers is" and of six contact bridges 2i?" and of six pairs of contacts 3t, 3% per phase. in other applications the number of contact carriers, contact bridges and of pairs of fixed contacts per phase may be smaller than six or larger than six. The fixed contacts 31, 3d of each phase and the contact bridges of each phase are arranged in form of a sector of a circle. The fixed contacts 32., at the ends of each such sector are main arcing contacts and the fixed contacts of each such sector arranged between main contacts are auxiliary arcing contacts to be connected to the switchinng resistors R R arranged in the lower portion of switch housing 2". FIG. 9 shows all the arcing contacts pertaining to one phase, omitting the arcing contacts of the other phases. The linkages operating the movable arcing contacts not shown have been indicated in FIG. 9 by d-ash-and-dot lines.

When a tap-changing operation has been completed, the main tap-changing arcing contacts which are designed to perform switching operations should preferably be shunted by main current carrying contacts which are specially designed to perform this particular duty, as distinguished from current switching duty. FIG. 12 fully illustrates the arrangement of the aforementioned main current carrying contacts. The fixed main current carrying cont-acts are also shown in FIG. 9.

Reference numeral 33" has been applied to indicate six movable main current carrying contacts. These contacts 33 are arranged remotely from the main and auxiliary switching or arcing contacts 31, 39 and at a lower level than the latter. The movable main current carrying contacts 33" form current-carrying bridges conductively interconnecting conductor bars 9 and angular main current carrying contacts 34''. The transfer switch comprises six fixed main current carrying contacts 34", a pair of such contacts for each phase of a three phase circuit. The phase groups of the movable main current carrying contacts and the fixed main current carrying contacts are angularly displaced degrees. FIG. 12 shows three movable main current carrying contacts 34 in the closed position thereof and three such contacts in the open position thereof. The fixed main current carrying contacts 34 are secured to the inner surface of cylindrical switch housing 2". Each fixed main current carrying contact 34 is conductively connected to a pair of terminals 5". FIG. 12 shows three groups of terminals 5", each of these three groups pertaining to one phase of a three phase circuit. The above groups of terminals 5" are angularly displaced deg.=120 deg. Terminals 5" are intended for connection of the transfer switch to a pair of taps of a tapped transformer winding such as, for instance, taps U and U of FIGS. 4-7. PEG. 12 shows to the right two movable main current carrying contacts 33" of which one is in the closed posit-ion and the other in the open position thereof. The closed contact 33" of FIG. 12 performs the function of shunting contact bridge 1' of FIG. 4 in the position of the parts shown in that figure. The open contact 33" of FIG. 12 performs the function of the shunting contact bridge 6 of FIG. 4 subsequent to engagement by that contact bridge of its cooperating fixed contacts 31, 3t i.e. following the step shown in FIG. 7 of a tap changing operation. As shown in FIG. 12 each movable main current carrying contact 33 is pivotally attached at 33a" to an operating lever 35". The operating levers 35" are pivot-ally secured at 35a to lower end plate 13'. Each pair of movable current carrying contacts 33" associated with one phase of a polyphase circuit is under the control of a lever 36 having a pair of pivotable operating arms. These arms are operatively related to one pair of contacts 33 pertaining to one phase of a polyphase circuit. Levers 36 are pivo-tally supported on the lower guide plate 8". Since the lower end plate 13" follows the rotary motions of shaft 11" rotary motions of the latter cause engagement of contacts 33 with, and dis engagement of contacts 33" from, conductive bars 9 and contacts 34".

The current path of the structure of FIGS. 8-12 is the same as explained in detail in connection with FIGS. 4-7. The current path begins at terminals extends through resistors R R R R includes lower arcing contacts 30, contact bridges 20" and upper arcing contacts 31". Contacts 31" are conductively connected to a conductive strap L arranged on the outside of housing 2 by conductors projecting through housing 2". Strap L is connected to flange element 6 which is the structural equivalent of lead lltltl of FIGS. 47 and terminals 4- are applied to connect flange element 6" to the neutral point of the system.

The sequence of operating steps of contact bridges 20" of the structure of FIGS. 8l2 is the same as the sequence of operating steps of the contact bridges 1', 2' 5', 6 of FIGS. 4-9 described in connection with these figures. The kinematic theory underlying the structure of FIGS. 8-12 is set forth in detail in United States Patent 2,680,796 to Bernhard Jansen, June 8, 1954, for Load Changeover Switch for Tapped Transformers Using a Combination of Contact Movements see particularly FIG. 5 and column 6, line 55 to column 7, line 23) and reference may be had to that patent for additional information regarding this subject.

It will be apparent from the foregoing that transfer switches embodying the present invention achieve a relatively high interrupting capacity or switching capacity without resorting to auxiliary arc-quenching means such as, for instance, magnetic blow-outs or forced oil circulation.

it will further be apparent from the foregoing that transfer switches embodying the present invention dispense entirely with flexible connections or braids for energizing the movable contact segments including contact bridges 20".

Since contact bridges 20 are insulated from their supports l all the movable parts within the transfer switch may be made of metal rather than of insulating material, which greatly contributes to the ruggedness of transfer switches embodying the present invention. The ruggedness of such transfer switches is due in particular to the presence of the squirrel-cage type structure comprising guide plates 7", and the three conductive bars 9".

The particular arrangement of the movable main current carrying cont-acts 53" shown makes the same readily accessible for servicing operations and renewal. The three conductive bars 9", in addition to providing a sturdy frame supporting the movable parts of the switch, oifer current paths of relatively large cross-section and minimal resistance for connecting taps of tapped polyph-ase transformer windings to the neutral point of the polyphase system.

it will be further apparent that the entire transfer switch is supported as a self-sustained structural unit at a single point, namely at the flange element 6". Upon removal of the transfer switch from the transformer tank with which it is normally associated and upon removal of the tap-changing or switch-over resistors R R the transfer switch structure proper may be withdrawn from housing 2" in downward direction upon loosening the supporting screws 10''.

Although I have shown and described a specific structure, it is to be clearly understood that the same was merely for the purpose of illustration, and that changes and modifications may readily be made by those skilled in the art without departing from the spirit and scope of the invention.

I claim as my invention:

1. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a plurality of pairs of spaced fixed contacts, said plurality of pairs of contacts including two outer pairs of fixed main contacts and inner pairs of auxiliary fixed contacts arranged between said two pairs of fixed main contacts;

(1')) a plurality of contact bridges each adapted to engage with and to part from, one of said plurality of pairs of fixed contacts, said plurality of contact bridges including two main contact bridges each adapted to engage with, and to part from, one of said two pairs of fixed main contacts, and said plurality of contact bridges further including auxiliary contact bridges each adapted to engage with, and to part from, one of said pairs of auxiliary fixed contacts;

(0) 'a 'pair of terminals for connecting said transfer switch to different taps of a transformer Winding, each of said pair of terminals being conductively connected to one of each said two pairs of fixed main contacts;

(at) a plurality of ohmic resistors each conductively connecting one of said pair of terminals to one auxiliary fixed contact of said pairs of auxiliary fixed contacts, said one auxiliary fixed contact being situated adjacent to one of the two ends of said plurality of contact bridges;

(2) means conductively interconnecting one of each of said pairs of auxiliary fixed contacts situated adjacent to the other of the two ends of said plurality of contact bridges; and

(f) a pair of leads conductively connecting one of said two pairs of fixed main contacts situated adjacent to said other of the two ends of said plurality of contact bridges to the fixed auxiliary contact cooperating with the auxiliary contact bridges immediately adjacent said two main contact bridges and situated adjacent to said other of the two ends of said plurality of contact bridges.

2. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a first line of spaced fixed contacts including a pair of fixed main contacts each arranged at the end of said first line and auxiliary fixed contacts ar ranged between said pair of main fixed contacts;

(b) a second line of spaced fixed contacts including a pair of main fixed contacts each arranged at the end of said second line and auxiliary fixed contacts arranged between said pair of main fixed contacts;

(0) a plurality of contact bridges each adapted to engage with, and to part from, one of said fixed contacts in said first line and one of said fixed contacts in said second line, said plurality of contact bridges including a pair of main contact bridges each adapted to cooperate with one of said pair of main contacts in said first line and one of said pair of main contacts in said second line, and said plurality of contact bridges further including aux iliary contact bridges each adapted to cooperate with one of said auxiliary contacts in said first line and one of said auxiliary contacts in said second line;

(0.) means for conductivcly interconnecting said auxiliary fixed contacts in said first line;

(e) a transformer winding having a pair of taps each directly conductively connected to said pair of main fixed contacts in said second line;

(f) a plurality of resistors each connecting one of said pair of taps to one of said auxiliary fixed contacts in said second line; and

(g) a pair of conductor means each connecting one of said pair of main fixed contacts in said first line to one of said plurality of resistors thereby shunting said one of said plurality of resistors across one of said pair of main contact bridges.

3. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) six parallel contact bridges including a pair of outer main contact bridges and four inner auxiliary contact bridges;

(b) a first group of fixed contacts including six contacts arranged adjacent one end of said six contact bridges and each adapted to be engaged by, and to be disengaged from, one of said six contact bridges, said first group including a pair of outer main contacts and four inner auxiliary contacts;

(c) a second group of fixed contacts including six contacts arranged adjacent the other end of said six contact bridges and each adapted to be engaged by, and to be disengaged from, one of said six contact bridges, said second group including a pair of outer main contacts and four inner auxiliary contacts;

(d) means for conductively interconnecting said four auxiliary contacts pertaining to said first group; (e) a transformer winding having a pair of taps each conductively connected to one of said pair of main contacts pertaining to said second group;

(f) a first pair of ohmic resistors each conductively connected "to one or" said pair of taps and to an auxiliary contact pertaining to said second group to establish a series connection with one of said auxil iary contact bridges;

(g) a second pair of ohmic resistors each conductively connected to one of said pair of taps and to an auxiliary contact pertaining to said second group to establish a series connection with one of said auxiliary contact bridges; and

(h) conductor means for shunting each of said first pair of ohmic resistors across one of said pair of main contact bridges.

4. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a plurality of pairs of spaced fixed contacts ar ranged at a predetermined level, said plurality of pairs of contacts including two outer pairs of fixed main contacts and inner pair of fixed auxiliary contacts arranged between said two pairs of fixed main contacts;

(b) a plurality of contact bridges each adapted to engage with, and to part from, one of said plurality of pairs of fixed contacts, said plurality of contact bridges including two main contact bridges each adapted to engage with, and to part from, one of said two pairs of fixed main contacts, and said plurality of contact bridges further including auxiliary contact bridges each adapted to engage with, and to part from, one of said pairs of fixed auxiliary contacts;

(c) a plurality of ohmic resistors arranged at a lower level than said predetermined level;

(d) a pair of terminals for connecting said transfer switch to difierent taps of a transformer winding, each of said pair of terminals being conductively connected to one fixed main contact of each of said two pairs of fixed main contacts;

(e) conductor means connecting each of said plural ity of resistors to one of said pair of terminals and in series with one of said pair of fixed auxiliary contacts and one of said auxiliary contact bridges;

(f) means conductively interconnecting the other of each of said pairs of fixed auxiliary contacts; and

(g) conductor means shunting one of said plurality of resistors across each of said two main contact bridges.

5. A transfer switch for tap-changing regulating transformers comprising in combination:

(a) a plurality of pairs of spaced fixed contacts, said plurality of pairs of contacts including two outer pairs of fixed main contacts and inner pairs of auxiliary fixed contacts arranged between said two pairs of fixed main contacts;

(12) a plurality of contact bridges each adapted to engage with, and part from, one of said plurality of pairs of fixed contacts, said plurality contact bridges including two main contact bridges each adapted to engage with, and to part from, one of said two pairs of fixed main contacts, and said plurality of contact bridges further including auxiliary contact bridges each adapted to engage with, and to part from, one of said pairs of auxiliary fixed contacts;

(0) a transformer winding including a pair of spaced taps;

(d) leads conductively connecting each of said pair of taps to one of said two pairs of fixed main contacts;

(6) leads conductively connecting each of said pair of taps by the intermediary of ohmic resistors to one of said fixed auxiliary contacts;

( means conductively interconnecting the other of each of said pairs of fixed auxiliary contacts; and (g) a pair of leads conductively connecting the other of said two pairs of fixed main contacts to one of said ohmic resistors thereby establishing a shunt current path including said one of said ohmic resistors across each of said two main contact bridges.

References Cited in the file of this patent UNITED STATES PATENTS 2,680,790 Jansen June 8, 1954 2,833,873 Jansen May 6, 1958 3,005,881 Ellsworth Oct. 24, 1961 3,014,999 Pensis Dec. 26, 1961 3,045,173 Wilson July 17, 1962 3,090,841 Piontkowski May 21, 1963 3,100,865 Nielsen Aug. 13, 1963 UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECT ION Patent No. 5,174,097 March'lo, 1965 Alexander Bleibtreu It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 31, for "transformer" read transfer column 5, line 67, after "formed" insert between column 10, line 31, for "other" read one Signed and sealed this 24th day of August 1965,

(SEAL) A tte st:

ERNEST W. SWIDER EDWARD J. BRENNER Attcsting Officer Commissioner of Patents UNITED STATES PATENT OFFICE I I CERTIFICATE OF CORRECT ION Patent No 3 ,l74, 09.7 March 16, 1965 Alexander Bleibtreu It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as Q corrected below.

Column 4, line 31, for "transformer" read transfer column 5, line 67, after "formed" insert between column l0, line-Bl, for "other" read one Signed and sealed this 24th day of August 1965.

(SEAL) A Host:

EDWARD J. BRENNER Commissioner of Patents ERNEST W. SWIDER Attesting Officer 

1. A TRANSFER SWITCH FOR TAP-CHANGING REGULATING TRANSFORMERS COMPRISING IN COMBINATION: (A) A PLURALITY OF PAIRS OF SPACED FIXED CONTACTS, SAID PLURALITY OF PAIRS OF CONTACTS INCLUDING TWO OUTER PAIRS OF FIXED MAIN CONTACTS AND INNER PAIRS OF AUXILIARY FIXED CONTACTS ARRANGED BETWEEN SAID TWO PAIRS OF FIXED MAIN CONTACTS; (B) A PLURALITY OF CONTACT BRIDGES EACH ADAPTED TO ENGAGE WITH AND TO PART FROM, ONE OF SAID PLURALITY OF PAIRS OF FIXED CONTACTS, SAID PLURALITY OF CONTACT BRIDGES INCLUDING TWO MAIN CONTACT BRIDGES EACH ADAPTED TO ENGAGE WITH, AND TO PART FROM, ONE OF SAID TWO PAIRS OF FIXED MAIN CONTACTS, AND SAID PLURALITY OF CONTACT BRIDGES FURTHER INCLUDING AUXILIARY CONTACT BRIDGES EACH ADAPTED TO ENGAGE WITH AND TO PART FROM, ONE OF SAID PAIRS OF AUXILIARY FIXED CONTACTS; (C) A PAIR OF TERMINALS FOR CONNECTING SAID TRANSFER SWITCH TO DIFFERENT TAPS OF A TRANSFORMER WINDING, EACH OF SAID PAIR OF TERMINALS BEING CONDUCTIVELY CONNECTED TO ONE OF EACH SAID TWO PAIRS OF FIXED MAIN CONTACTS; 